The present invention relates to a method of cleaning an electronic device having a component containing a refractory metal such as tungsten (W) and to a method of fabricating the same. More particularly, it relates to a method of cleaning an electronic device having a polymetal gate electrode structure (such as W/WNx/Poly-Si) or a metal gate electrode structure (such as W/WNx) for reducing the resistance of the gate electrode of a MOS transistor and to a method of fabricating the same.
In recent years, increasing miniaturization, higher integration density, higher-speed operation, and lower power consumption has been required of a VLSI device.
In the process of fabricating a VLSI device, the operating speed of the VLSI device is further increased by reducing the resistance of the gate electrode of a MOS transistor. To reduce the resistance of the gate electrode of the MOS transistor, there has been developed a polymetal gate electrode or metal gate electrode using a metal not containing silicon, specifically a refractory metal, as a replacement of a conventional polysilicon gate electrode or silicide gate electrode.
As an exemplary structure of the polymetal gate electrode, a structure in which W/WNx/Poly-Si is deposited on a gate oxide film or a structure in which W/TiN/Poly-Si is deposited on a gate oxide film has been used.
As an exemplary structure of the metal gate electrode, a structure in which W/WNx is deposited on a gate oxide film or a structure in which W/TiN is deposited on a gate oxide film has been used.
As the refractory metal composing the polymetal gate electrode or metal gate electrode, tungsten has been used predominantly (Monthly Semiconductor World, pp.76-81, 1998, 9).
In cleaning an electronic device having a conventional polysilicon gate electrode or silicide gate electrode, a cleaning solution which is a mixture of an acidic or alkaline solution and aqueous hydrogen peroxide (H2O2) has been used predominantly to remove a particle (having a diameter of about 10 xcexcm or less), resist residue, a polymer, or a metal. Such a method of cleaning an electronic device is generally known as an RCA cleaning method.
However, if an electronic device having a polymetal gate electrode, metal gate electrode, or the like containing a refractory metal such as tungsten is cleaned by such a conventional cleaning method as the RCA cleaning method, tungsten or the like composing the gate electrode is dissolved disadvantageous, so that the reliability of the electronic device is reduced.
In view of the foregoing, it is an object of the present invention to ensure cleaning of an electronic device, while preventing the dissolution of a refractory metal such as tungsten contained in a component of the electronic device.
The present inventors have examined the cause of the dissolution of tungsten contained in the component of the electronic device when a conventional cleaning method is used.
Referring to FIGS. 4(a) to 4(c), a description will be given to the case of forming a polymetal gate electrode containing tungsten on a substrate and then cleaning the substrate in accordance with the conventional cleaning method. In the present specification, a substrate formed with a component such as a gate electrode will be termed an electronic device.
First, as shown in FIG. 4(a), a gate oxide film 2 is formed by thermal oxidation on a silicon substrate 1. Then, a polysilicon (Poly-Si) film 3A, a tungsten nitride (WNx) film 3B, and a tungsten film 3C as the materials of a polymetal gate electrode are deposited successively on the gate oxide film 2, followed by a silicon nitride film 4 deposited on the tungsten film 3C. Subsequently, dry etching is performed successively with respect to the silicon nitride film 4, the tungsten film 3C, the tungsten nitride film 3B, and the polysilicon film 3A by using a resist pattern (not shown) covering a region in which a gate electrode is to be formed as a mask, thereby forming a polymetal gate electrode 3 composed of the polysilicon film 3A, the tungsten nitride film 3B, and the tungsten film 3C on the silicon substrate 1 with the gate oxide film 2 interposed therebetween. Thereafter, the resist pattern is removed by ashing.
Next, the silicon substrate 1 is cleaned by sequentially using a first cleaning solution composed of a SPM solution (a solution mixture of sulfuric acid (H2SO4) and aqueous hydrogen peroxide) and a second cleaning solution composed of an APM solution (a solution mixture of aqueous ammonium (NH4OH), aqueous hydrogen peroxide, and water).
During the cleaning process, as shown in FIG. 4(b), the tungsten nitride film 3B and the tungsten film 3C, each composing the polymetal gate electrode 3, are etched in a direction parallel to the silicon substrate 1.
The present inventors tried cleaning the silicon substrate 1 by increasing the respective concentrations of aqueous hydrogen peroxide contained in the SPM solution and in the APM solution.
As a result, as shown in FIG. 4(c), the tungsten nitride film 3B and the tungsten film 3C, each composing the polymetal gate electrode 3, were entirely dissolved to disappear.
This proves that aqueous hydrogen peroxide contained in the conventional cleaning solution is the cause of the dissolution of tungsten contained in the component of the electronic device.
The present inventors also assumed the formula representing the chemical reaction between tungsten and aqueous hydrogen peroxide to be
xe2x80x83W+2H2O2xe2x86x92WO2+2H2O (Oxidation of Tungsten)
2WO2+6H2O2xe2x86x92H2W2O11+5H2O (Dissolution of Tungsten)
3H2W2O11+7H2O xe2x86x922H2W3O1630 8H2O (Dissolution of Tungsten).
It may be considered that, if the electronic device having the component containing tungsten is cleaned with the cleaning solution containing aqueous hydrogen peroxide, the chemical reaction proceeds catalytically between tungsten and aqueous hydrogen peroxide in accordance with the foregoing chemical reaction formula, so that tungsten contained in the component of the electronic device is dissolved.
The present invention has been achieved based on the foregoing findings. Specifically, a first method of cleaning an electronic device according to the present invention comprises the step of: cleaning an electronic device having a component containing tungsten by using a cleaning solution composed of an acidic solution which does not substantially contain aqueous hydrogen peroxide or an alkaline solution which does not substantially contain aqueous hydrogen peroxide.
In accordance with the first cleaning method, the electronic device is cleaned by using the cleaning solution composed of the acidic solution which does not substantially contain aqueous hydrogen peroxide or the alkaline solution which does not substantially contain aqueous hydrogen peroxide. Compared with the case where a cleaning solution containing aqueous hydrogen peroxide is used, the etching rate for tungsten can be reduced significantly and particles, resist residue, a polymer, or the like can be removed thoroughly. This ensures cleaning of the electronic device, while preventing the dissolution of tungsten contained in a component of the electronic device.
In the present specification, the cleaning solution which does not substantially contain aqueous hydrogen peroxide is defined as a cleaning solution which contains aqueous hydrogen peroxide (at a concentration of 30wt %) at a volume ratio of less than about 0.2%.
In the first cleaning method, the cleaning solution is preferably a solution mixture of tetramethyl ammonium hydroxide and water.
In the arrangement, the etching rate for tungsten can be reduced significantly compared with the case where a cleaning solution containing aqueous hydrogen peroxide is used and particles, resist residue, a polymer, or the like can be removed thoroughly.
In this case, if a concentration of tetramethyl ammonium hydroxide in the solution mixture is adjusted to be in the range of 0.01 to 5.0wt %, the foregoing effects are achieved positively.
In the first cleaning method, the cleaning solution is preferably ozone-containing water.
In the arrangement, the etching rate for tungsten can be reduced significantly compared with the case where a cleaning solution containing aqueous hydrogen peroxide is used and particles, resist residue, a polymer, or the like can be removed thoroughly.
In this case, if a concentration of ozone in the ozone-containing water is adjusted to be in the range of 0.1 to 100 ppm, the foregoing effects are achieved positively.
In the first cleaning method, the cleaning solution is preferably aqueous ammonia.
In the arrangement, the etching rate for tungsten can be reduced significantly compared with the case where a cleaning solution containing aqueous hydrogen peroxide is used and particles, resist residue, a polymer, or the like can be removed thoroughly.
In this case, if a concentration of ammonia in the aqueous ammonia is adjusted to be in the range of 0.1 to 5.0wt %, the foregoing effects are achieved positively.
In this case, if ozone is added to the aqueous ammonia, the foregoing effects are achieved more positively.
In the first cleaning method, the cleaning solution is preferably a solution mixture of hydrofluoric acid or sulfuric acid and water.
In the arrangement, the etching rate for tungsten can be reduced significantly compared with the case where a cleaning solution containing aqueous hydrogen peroxide is used and particles, resist residue, a polymer, or the like can be removed thoroughly.
In this case, if ozone is added to the solution mixture, the foregoing effects are achieved more positively.
A second method of cleaning an electronic device according to the present invention comprises the step of: cleaning an electronic device having a component containing tungsten by sequentially using two or more of a solution mixture of tetramethyl ammonium hydroxide and water, ozone-containing water, aqueous ammonia, aqueous ammonia containing ozone, a solution mixture of hydrofluoric acid and water, a solution mixture of hydrofluoric acid and water containing ozone, a solution mixture of sulfuric acid and water, and a solution mixture of sulfuric acid and water containing ozone.
In accordance with the second cleaning method, the electronic device is cleaned by sequentially using two or more of the solution mixture of tetramethyl ammonium hydroxide and water, the ozone-containing water, the aqueous ammonia, the aqueous ammonia containing ozone, the solution mixture of hydrofluoric acid and water, the solution mixture of hydrofluoric acid and water containing ozone, the solution mixture of sulfuric acid and water, and the solution mixture of sulfuric acid and water containing ozone. Compared with the case where a cleaning solution containing aqueous hydrogen peroxide is used, the etching rate for tungsten can be reduced significantly and particles, resist residues, a polymer, or the like can be removed thoroughly. This ensures cleaning of the electronic device, while preventing the dissolution of tungsten contained in a component of the electronic device.
A third method of cleaning an electronic device according to the present invention comprises the step of: cleaning an electronic device having a component containing tungsten by sequentially using a first cleaning solution composed of a solution mixture of hydrofluoric acid and water, a second cleaning solution composed of ozone-containing water, and a third cleaning solution composed of a solution mixture of tetramethyl ammonium hydroxide and water.
In accordance with the third cleaning method, the electronic device is cleaned by sequentially using the first cleaning solution composed of the solution mixture of hydrofluoric acid and water (hereinafter referred to as a DHF solution), the second cleaning solution composed of the ozone-containing water (hereinafter referred to as aqueous O3), and the third cleaning solution composed of the solution mixture of tetramethyl ammonium hydroxide and water (hereinafter referred to as a TMAH solution). Compared with the case where a cleaning solution containing aqueous hydrogen peroxide is used, the etching rate for tungsten can be reduced significantly and particles, resist residue, a polymer, or the like can be removed thoroughly. This ensures cleaning of the electronic device, while preventing the dissolution of tungsten contained in a component of the electronic device.
A first method of fabricating an electronic device according to the present invention comprises the steps of: forming, on a substrate, a multilayer film including at least a refractory metal film; performing dry etching with respect to the multilayer film by using a mask pattern covering a gate electrode formation region of a first-conductivity-type transistor formation region and thereby forming a gate electrode composed of the multilayer film; implanting a second-conductivity-type impurity into the first-conductivity-type transistor formation region by using a resist pattern covering a second-conductivity-type transistor formation region and the gate electrode as a mask; and removing the resist pattern by ashing and cleaning the substrate by sequentially using a first cleaning solution composed of a solution mixture of hydrofluoric acid and water, a second cleaning solution composed of ozone-containing water, and a third cleaning solution composed of a solution mixture of tetramethyl ammonium hydroxide and water.
In accordance with the first fabrication method, the substrate formed with the gate electrode is cleaned by sequentially using the first cleaning solution composed of the DHF solution, the second cleaning solution composed of the aqueous O3, and the third cleaning solution composed of the TMAH solution. Compared with the case where a cleaning solution containing aqueous hydrogen peroxide is used, the etching rate for a refractory metal can be reduced significantly and particles, resist residue, a polymer, or the like can be removed thoroughly. This ensures cleaning of the substrate, while preventing the dissolution of a refractory metal contained in the gate electrode, thereby providing an electronic device with high reliability.
Moreover, since the first fabrication method removes particles, resist residue, a polymer, or the like together with the oxide film formed on the substrate or on the refractory metal film under the lift-off effect or the like exerted by the cleaning process using the DHF solution (first cleaning solution), forms an oxide film for preventing the production of stains (water marks) on the substrate by the cleaning process using the aqueous O3 (second cleaning solution), and removes remaining microfine particles by the cleaning process using the TMAH solution (third cleaning solution), the reliability of the electronic device is further improved.
A second method of fabricating an electronic device according to the present invention comprises the steps of: forming a refractory metal film on a substrate; performing dry etching with respect to the refractory metal film by using a resist pattern covering a gate electrode formation region and thereby forming a gate electrode composed of the refractory metal film; and removing the resist pattern by ashing and cleaning the substrate by sequentially using a first cleaning solution composed of a solution mixture of hydrofluoric acid and water, a second cleaning solution composed of ozone-containing water, and a third cleaning solution composed of a solution mixture of tetramethyl ammonium hydroxide and water.
In accordance with the second fabrication method, the substrate formed with the gate electrode is cleaned by sequentially using the first cleaning solution composed of the DHF solution, the second cleaning solution composed of the aqueous O3, and the third cleaning solution composed of the TMAH solution. Compared with the case where a cleaning solution containing aqueous hydrogen peroxide is used, the etching rate for a refractory metal can be reduced significantly and particles, resist residue, a polymer, or the like can be removed thoroughly. This ensures cleaning of the substrate, while preventing the dissolution of a refractory metal contained in the gate electrode, thereby providing an electronic device with high reliability.
Moreover, since the second fabrication method removes particles, resist residue, a polymer, or the like together with the oxide film formed on the substrate or on the refractory metal film under the lift-off effect or the like exerted by the cleaning process using the DHF solution (first cleaning solution), forms an oxide film for preventing the production of stains (water marks) on the substrate by the cleaning process using the aqueous O3 (second cleaning solution), and removes remaining microfine particles by the cleaning process using the TMAH solution (third cleaning solution), the reliability of the electronic device is further improved.
In the first or second fabrication method, the gate electrode preferably has a polymetal gate electrode structure or a metal gate electrode structure.
This allows the formation of an electronic device having a high-performance polymetal gate electrode or metal gate electrode.
A third method of fabricating an electronic device according to the present invention comprises the steps of: forming a first electrode structure and a second electrode structure on a first-conductivity-type MOSFET formation region and a second-conductivity-type MOSFET formation region of a substrate, respectively; implanting a second-conductivity-type impurity into the first-conductivity-type MOSFET formation region by using, as a mask, a first resist pattern covering the second-conductivity-type MOSFET formation region including the second electrode structure and the first electrode structure to form a first source region and a first drain region in the first-conductivity-type MOSFET formation region; removing the first resist pattern by ashing using an oxygen plasma and cleaning the substrate by sequentially using a first cleaning solution composed of a solution mixture of hydrofluoric acid and water, a second cleaning solution composed of ozone-containing water, and a third cleaning solution composed of a solution mixture of tetramethyl ammonium hydroxide and water; implanting a first-conductivity-type impurity into the second-conductivity-type MOSFET formation region by using, as a mask, a second resist pattern covering the first-conductivity-type MOSFET formation region including the first electrode structure and the second electrode structure to form a second source region and a second drain region in the second-conductivity-type MOSFET formation region; and removing the second resist pattern by ashing using an oxygen plasma and cleaning the substrate by sequentially using the first cleaning solution composed of the solution mixture of hydrofluoric acid and water, the second cleaning solution composed of the ozone-containing water, and the third cleaning solution composed of the solution mixture of tetramethyl ammonium hydroxide and water, each of the first and second electrode structures having a multilayer structure composed of a polysilicon film and a refractory metal film.
In accordance with the third fabrication method, the substrate formed with the electrode structures is cleaned by sequentially using the first cleaning solution composed of the DHF solution, the second cleaning solution composed of the aqueous O3, and the third cleaning solution composed of the TMAH solution. Compared with the case where a cleaning solution containing aqueous hydrogen peroxide is used, the etching rate for a refractory metal can be reduced significantly and particles, resist residue, a polymer, or the like can be removed thoroughly. This ensures cleaning of the substrate, while preventing the dissolution of a refractory metal contained in the electrode structures, thereby providing an electronic device with high reliability.
Moreover, since the third fabrication method removes particles, resist residue, a polymer, or the like together with the oxide film formed on the substrate or on the refractory metal film under the lift-off effect or the like exerted by the cleaning process using the DHF solution (first cleaning solution), forms an oxide film for preventing the production of stains (water marks) on the substrate by the cleaning process using the aqueous O3 (second cleaning solution), and removes remaining microfine particles by the cleaning process using the TMAH solution (third cleaning solution), the reliability of the electronic device is further improved.
A fourth method of fabricating an electronic device according to the present invention comprises the steps of: forming a first electrode structure and a second electrode structure on a first-conductivity-type MOSFET formation region and a second-conductivity-type MOSFET formation region of a substrate, respectively; implanting a second-conductivity-type impurity into the first-conductivity-type MOSFET formation region by using, as a mask, a first resist pattern covering the second-conductivity-type MOSFET formation region including the second electrode structure and the first electrode structure to form a first source region and a first drain region in the first-conductivity-type MOSFET formation region; removing the first resist pattern by ashing using an oxygen plasma and cleaning the substrate by sequentially using a first cleaning solution composed of a solution mixture of hydrofluoric acid and water, a second cleaning solution composed of ozone-containing water, and a third cleaning solution composed of a solution mixture of tetramethyl ammonium hydroxide and water; implanting a first-conductivity-type impurity into the second-conductivity-type MOSFET formation region by using, as a mask, a second resist pattern covering the first-conductivity-type MOSFET formation region including the first electrode structure and the second electrode structure to form a second source region and a second drain region in the second-conductivity-type MOSFET formation region; and removing the second resist pattern by ashing using an oxygen plasma and cleaning the substrate by sequentially using the first cleaning solution composed of the solution mixture of hydrofluoric acid and water, the second cleaning solution composed of the ozone-containing water, and the third cleaning solution composed of the solution mixture of tetramethyl ammonium hydroxide and water, each of the first and second electrode structures containing a metal.
In accordance with the fourth fabrication method, the substrate formed with the electrode structures is cleaned by sequentially using the first cleaning solution composed of the DHF solution, the second cleaning solution composed of the aqueous O3, and the third cleaning solution composed of the TMAH solution. Compared with the case where a cleaning solution containing aqueous hydrogen peroxide is used, the etching rate for a metal can be reduced significantly and particles, resist residue, a polymer, or the like can be removed thoroughly. This ensures cleaning of the substrate, while preventing the dissolution of a metal contained in the electrode structures, thereby providing an electronic device with high reliability.
Moreover, since the fourth fabrication method removes particles, resist residue, a polymer, or the like together with the oxide film formed on the substrate or on the metal film under the lift-off effect or the like exerted by the cleaning process using the DHF solution (first cleaning solution), forms an oxide film for preventing the production of stains (water marks) on the substrate by the cleaning process using the aqueous O3 (second cleaning solution), and removes remaining microfine particles by the cleaning process using the TMAH solution (third cleaning solution), the reliability of the electronic device is further improved.